Body Impolitic

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Healthy Eating: Most of What We Already Knew Is Wrong

Laurie and Debbie say:

A major science story on the consequences of what we believed was healthy eating has been simultaneously buried and distorted for the press by the National Institutes of Health, to a degree that even the two us find astonishing.

It took the detective powers of Sandy Swarcz at Junk Food Science to thoroughly expose this one. Her analysis is in two parts, and both are nearly compulsory reading.

Here’s the short version from Sandy:

It was named the Women’s Health Initiative (WHI) Dietary Modification Trial. A total of 48,835 postmenopausal women (the age most associated the risk for developing heart disease and cancers) were randomly assigned (with each group well matched) to either their regular unrestricted diet or to a “healthy” diet that was low-fat (20% fat) and high fiber, with at least 5 servings of fruits and vegetables, and 6 servings of grains a day.

More than 8 years later, there was no difference in the incidences of breast cancer, colon cancer, heart attacks or strokes among those who ate “healthy” and those who ate whatever they pleased.

We’ll go a little further into the science in a minute, but first let’s look at how this has been reported.

First of all, you know that if they had found (as they expected to), clearcut positive results from the “healthy” diets, you wouldn’t have been able to walk down the street or turn on a radio or television without hearing endlessly about it. But since they found out we can eat what we want, here’s what happened.

The Women’s Health Initiative is a program of the U.S. government’s National Institutes of Health. Its own site has issued exactly one press release: “Low-Fat Dietary Pattern May Lower Risk of Ovarian Cancer — The WHI Dietary Modification Trial.” They are not, in fact, honest about the statistical significance of the findings, although the Journal of the National Cancer Institute, which takes its information, and its spin, from the WHI, does admit “the overall ovarian cancer hazard ratio (HR) was not statistically significant.”

The media gets its science news largely from press releases and journal articles. Since this is all that the study’s creators are releasing, the overwhelming silence is somewhat less surprising.

Nonetheless, the news should be all over the headlines, based on the Journal of the American Medical Association articles which Sandy mentions. The only conclusion we can draw is no one likes these answers, so no one reports the news. What we don’t understand is why the fast food restaurants and prepared food companies aren’t using these figures as advertisements!

Here are some of the hard numbers, and some explanations.

Ã¢â‚¬Å“a dietary intervention that reduced total fat intake and increased intakes of vegetables, fruits, and grains did not significantly reduce the risk of CHD, stroke, or CVD in postmenopausal women.Ã¢â‚¬Â

Ã¢â‚¬Å“We found no evidence that lower intake of total fat or specific major types of fat was associated with a decreased risk of breast cancer.Ã¢â‚¬Â In fact, women who had eaten the lowest fat diets before the study began (i.e, probably before menopause) had slightly higher risks for breast cancer than women with the highest-fat diets; the women who with the biggest reductions in fat in their diets were at the highest risks for breast cancer. (None of these numbers were statistically significant, however.)

Ã¢â‚¬Å“A low-fat dietary pattern intervention did not reduce the risk of colorectal cancer in postmenopausal women during 8.1 years of follow-up.Ã¢â‚¬Â

What’s more, there were no significant changes in the weight of either group.

In her second post, Sandy makes a couple of important points.

Other things that made no difference in risks for the invasive cancers between the dieters and control group included: diabetes; dietary fats, grains, or fruits and vegetables intake (in separate analyses); physical activity (from less than 1.5 to more than 14.8 METS/week); and BMI. Yes, despite all of the fears about body weights, incidences of invasive cancers were not significantly different among women who were fat (in the Ã¢â‚¬Å“overweight,Ã¢â‚¬Â Ã¢â‚¬Å“obeseÃ¢â‚¬Â and even Ã¢â‚¬Å“morbidly obeseÃ¢â‚¬Â medical categories).

One of Junk Food Science’s particularly important qualities is Sandy’s ability to explain scientific and statistical concepts clearly. Speaking about the slightly increased numbers on liver cancer, she says:

It is important to remember that relative risks or odds are not the same as actual incidences of disease; so, that 130% higher risk of liver cancer obviously does not mean that 130% of women got that cancer. In actuality, the total incidences of liver cancer was 0.0368%, with only 3 actual cases difference between the 48,835 women. As the researchers noted, it’s not statistically greater than a random toss of the dice.

Of course, the study only tracked women, and only focused on the post-menopausal period. There are more studies to be done. In the meantime, however, this is an astonishingly strong brick in the structure of “be relaxed about what you eat and eat a wide variety of what tastes good to you.”

In a discussion about this article (and several others, mostly Sandy’s) in a personal LJ, one mainstream person (science writer and interviewer) tried to say that “all this proved was that *low-fat* diets don’t work, and besides which the low-fat fad was over anyway.” I suggested this constituted “moving the goalposts,” but didn’t get an adequate answer IMO.

I think it’s important to note that this study says nothing useful about the value of a low saturated fat, high vegetable and fruit diet for people, like myself, who already HAVE heart disease and are trying through diet to lower cholesterol and counter the inflammatory processes involved in heart disease. Once you have it, especially if you have had a heart attack or other incident, a low saturated fat diet makes a lot of sense.

Another comment regarding low-fat and heart disease: there is good enough that a 20% “low fat” diet is actually still too high in fat to make a clear difference for people who already have heart disease, and that 6 servings of grains per day is a useless recommendation and adds nothing to the pursuit of health if the grains people choose to eat are nutritionally empty.

Have any of you read the Gary Taubes book on nutrition science yet? If so, I’m curious what you think. Matt is reading it and is pretty impressed.

I take all nutrition studies with a grain of salt (har har) because there are too many variables to control, and the studies are inevitably based on self-reporting, which is notoriously inaccurate. Do you know anybody who, assigned to a specific diet for a study, would follow it consistently (not perfectly, just consistently) for 8 years? I don’t know many. Even 6 months would be impressive, if it’s a diet that’s significantly different a) from the way they were eating before and b) from their family and social group’s eating habits. And if they’re not heavily motivated by a medical condition or something? I just don’t buy it. This is why I buy very little nutritional advice, beyond “eat real food.”

Matt already posted his review of Taubes on his “Books I read in 2007” page. Gina Kolata reviewed it for the Times and agreed with him on many things, but not his conclusion that carbohydrates are addictive and dangerous.

I am skeptical about any long-term studies based on self-reported data, especially if they have to do with food, weight, money, or sex.